The technology of manipulating minute volumes of biological and chemical fluids is widely referred to as microfluidics. The realized and potential applications of microfluidics include disease diagnosis, life science research, biological and/or chemical sensor development, and others appreciated by those skilled in the art.
A microfluidic structure including a substrate having one or more microfluidic channels or pathways and a cover plate or a second or more substrates with fluid pathways that may or may not be interconnected, may commonly be referred to as a microfluidic chip or cartridge. Highly integrated microfluidic chips are sometimes called “labs on a chip”.
Microfluidic structures or devices are commonly made from polymeric, “plastic” materials. Polymeric microfluidic structures have advantageous low material costs and the potential for mass production. However, the fabrication of polymeric microfluidic chips presents a variety of challenges. For example, microfluidic chips may contain sealed microstructures. These can be formed by enclosing a substrate having a pre-fabricated fluid pathway or other microfeatures with a thin cover plate, or with one or more additional substrates to form a three-dimensional fluid network. The pathways or other microstructures have typical dimensions in the range of micrometers to millimeters. This multilayer microfluidic structure is integrated, or joined together, by various conventional techniques. These techniques include thermal, ultrasonic and solvent bonding. Unfortunately, these techniques frequently alter the mated surfaces and yield distorted or completely blocked microfluidic pathways due, for example, to the low dimensional rigidity of polymeric materials under the aforementioned bonding conditions.
The use of adhesive lamination may circumvent some of these potential difficulties by avoiding the use of excessive thermal energy or strong organic solvents. Conventional lamination systems employ opposing cylindrical rollers. The substrate materials for lamination are fed through a gap between the two moving rollers, which apply pressure to the leading edge of the stacked materials and bonds them together as they pass through the system. This process is an effective means to bond a flexible film to a substrate without entrapment of air bubbles, while providing minimum deformation to the laminated product. However, the curved surfaces of roller-based systems are not optimal for the lamination of rigid substrates. For example, such substrates may lack the flexibility required to feed through moving rollers in a manner that maintains the precise substrate registration critical for ensuring the integrity of the integrated microfluidic features.
Alternative systems and methods for lamination of rigid substrates include planar press or “hinge” systems in which substrates are stacked, or “sandwiched”, between upper and lower platforms prior to application of a laminating force. One considerable drawback to this approach in the fabrication of microfluidic devices is the entrapment of air between the stacked substrates during lamination, resulting in deformations, such as bubbles or voids, in the final product. Such deformations may significantly compromise the function of the laminated microfluidic device, particularly when they arise in features such as fluidic channels or optical display windows. Accordingly, embodiments of the invention are directed to methods and apparatus for lamination of rigid structures that address these recognized shortcomings of the current state of technology, and which provide further benefits and advantages as those persons skilled in the art will appreciate.